[Ron Schotts Geology Home Companion Blog] I don’t personally have any detailed knowledge of the geology there (wrong side of the San Andreas in that region), but looking at the Santa Cruz 1:250,000 geologic map it appears to be constituted primarily of Pliocene marine rocks (probably not real strong stuff) at the northwest end and Pliocene and Pleistocene nonmarine rocks further south. These are all fairly young (geologically) and presumably are only weakly lithified - making them prime candidates for landsliding.

[Reflexions.typepad.com] Reflexions: Footfalls (Ultralight Backpacking): In ways that were almost mystical, Tom could read the tides of rock the way ancient mariners read the sea. It was both an education and an honor to walk with him in the canyons of his native country.